1. Field of the Invention
The invention relates to an impact tool that performs a predetermined operation on a workpiece at least by a linear movement of a tool bit in an axial direction.
2. Description of the Related Art
Japanese non-examined laid-open Patent Publication No. 2006-159376 discloses an impact tool in which a bit holding device is mounted onto a front end portion of a tool holder and holds the hammer bit inserted into the tool holder. In the bit holding device, a cylindrical outer shell component forms an outer shell of the bit holding device and is fitted onto the tool holder into which the hammer bit is inserted so as to cover the front end portion of the tool holder. Further, a stopper in the form of a ring spring is fitted on the tool holder and prevents the outer shell component from slipping out of the tool holder.
In the above-described known construction, the ring spring may open by impact caused by idle driving of the impact tool (when the impact tool is driven in a state in which the hammer bit is not pressed against the workpiece). If such occurs repeatedly, the ring spring may be worn and damaged. Therefore, in the above-described impact tool, load is applied to the outer shell component in its axial direction by using a tool specifically designed for this purpose, so that a ring-like cushioning material (rubber) disposed within the outer shell component is compressively deformed. In this state, a metal washer and then a ring spring are fitted onto the tool holder, and an inner tapered surface of the washer is held in contact with the ring spring.
In this manner, the ring spring is fixed such that it is prevented from opening in the radial direction. Such a structure needs cumbersome assembling and it is not rational as an opening prevention structure for the ring spring. In this point, further improvement is required.